The present invention is directed to an expansion dowel formed by an expansion sleeve and an expansion member rolled from a section of sheet metal with the axially extending edges of the expansion sleeve forming a butt joint and with the inside surface of the sleeve being threaded from its trailing end for applying a load to the sleeve. Further, the sleeve has a recess adjacent its leading end in which the expansion member is held with the sides of the recess converging in the direction the leading end.
Expansion dowels including an expansion sleeve rolled from sheet metal are distinguished particularly by low costs. A known expansion dowel of this type is fabricated in one piece with a wedge-shaped expansion member formed in the sleeve and connected to it by a web. The web can be broken when the expansion of the sleeve is commenced. The expansion member, with the web broken, is driven forwardly through an opening in the wall of the expansion sleeve with the opening narrowing in a wedge-shaped manner toward the leading end of the sleeve, that is, the end first inserted into a borehole in which the expansion dowel is anchored.
A thread is formed in the trailing end section of the expansion sleeve for applying a load or force on the dowel after it is anchored in place. The thread can be formed in a stamping operation before the section of sheet metal is rolled into the expansion sleeve.
When the expansion sleeve is rolled there is the problem that the individual thread turns are not properly aligned in the axial direction of the sleeve along the butt joint formed by the axially extending edges of the sheet metal section. Such a problem may interfere with the insertion of the threaded bolt into the thread in the sleeve. Another problem in this known dowel is that the forces acting radially on the inside of the expansion sleeve due to the force applied by a threaded bolt, tend to widen the sleeve, if the borehole receiving the expansion dowel is diametrically oversized or if the receiving material in which the borehole is formed is soft and thus excessively yielding. To eliminate this problem it has been proposed to connect the adjacent axially extending edges forming the butt joint by soldering or welding. With such an arrangement there is the problem if the thread turns are misaligned that the misalignment is fixed. The insertion of the bolt into the threaded section of the expansion sleeve is, as a result, difficult to effect.